Method of bleaching sulfonate surfactants

ABSTRACT

ALKYARLY SULFONATE SURFACTANTS ARE BLEACHED BY REACTING THEIR AQUEOUS SOLUTIONS WITH AN INORGANIC HYPOHALITE AND AN INORGANIC PERMANGANATE, SEQUENTIALLY OR IN COMBINATION. THE PROCESS IS PARTICULARLY ADAPTABLE TO DECOLORIZING HIGHER ALKYL DIPHENYL ETHER DISULFONATES USING SODIUM HYPOCHLORITE AND POTASSIUM PERMANGANATE AS THE BLEACHING AGENTS.

ul-le-Ya 3,677,952 METHOD OF BLEACHING SULFONATE SURFACTANTS Lowell B. Lindy, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich. No Drawing. Filed Oct. 2, 1970, Ser. No. 77,745

Int. Cl. Clld 7/54 U.S. Cl. 252-94 7 Claim! ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relates to a process whereby a new combination of known bleaching agents is applied to a crude sulfonate surfactant to obtain unexpectedly effective decolorization and it relates also to the bleached surfactant product.

Many substances including textiles, paper pulp, vegetable oils, and others have been treated with inorganic bleaching agents such as hypochlorites, hypobromites, permanganates, and peroxides to remove undesirable color. Bleaching agents such as these have also been applied to crude organic sulfonate surfactants. These surfactants are often undesirably contaminated with color bodies or colored byproducts formed during the manufacturing process which usually includes both alkylation and sulfonation reactions. For example, Sylvester, U.S. 2,738,- 365 describes the use of alkali hypochlorite to improve the color of alkyl aryl sulfonates and Wulif et al., U.S. 3,142,691 disclose the use separately of various bleaching agents including hypochlorite, permanganate, and dichromate to reduce the color of sulfonated fatty acids and their derivatives. Some bleaching agents have been used for the purpose in combination. Thus, Schurman, U.S. 2,804,466 shows the use of hypochlorite and peroxide together to bleach sulfated and sulfonated anionic surfactants.

SUMMARY OF THE INVENTION It has now been found that color is removed with unexpected efiiciency from alkyl aryl sulfonate surfactants when aqueous solutions of these substances are bleached by any combination of the steps:

(1) reacting by contacting an inorganic hypohalite with the solution, and

(2) reacting by contacting an inorganic permanganate with the solution and separating the resultant precipitated manganese oxide.

Unexpectedly, the two bleaching agents in combination provide significantly better bleaching than any quantity of either bleaching agent alone. Also, the order in which the steps are carried out makes little difference in the results obtained, and in fact, substantially the same results are also obtained when the two bleaching compounds are added more or less simultaneously.

DETAILED DESCRIPTION The process is applicable to any of the well known class of alkyl aryl sulfonate surfactants. This class is characterized by the presence of at least one higher alkyl substituent on the aromatic nucleus, higher alkyl being defined as defining a radical of 8-18 carbon atoms, either 3,677,952 Patented July 18, 1972 linear or branched in its carbon backbone, and one to two sulfonate groups per aromatic nucleus. Representative of this class are dodecylbenzenesulfonic acid, octadecylnaphthalenesulfonic acid, decyltotluenesulfonic acid, decyldiphenyl ether disulfonic acid, dodecyldiphenyl ether disulfonic acid, dodecylchlorodiphenyl ether disulfonic acid, and the sodium and potassium salts of these compounds.

The process is particularly adapted to eflicient decolorizing of alkyldiphenyl ether disulfonates having an average of about 1-1.3 alkyl groups of 8-18 carbon atoms and an average of about 1.6-2 sulfonate groups per diphenyl ether nucleus.

By the terms inorganic hypohalite and inorganic per manganate are meant hypochlorous acid, hypobromous acid, perrnanganic acid and the anhydrides and watersoluble inorganic salts of these, particularly the sodium and potassium salts. In practice, sodium hypochlorite and potassium permanganate are used since these are cheapest and most readily available. Equivalents of potassium permanganate in this process include sodium permanganate, calcium permanganate, permanganic acid (in aqueous solution), and manganese heptoxide. Hypohalite equivalents include sodium hypobromite, calcium hypochlorite, hypobromous acid, potassium hypochlorite, and chlorine monoxide. Many of these can only be used in aqueous solution.

The hypohalite bleaching step is preferably carried out with moderate heating, that is to say, at about 40l00 C. and for a bleaching time of about 0.1-2 hours. The quantity of hypohalite can vary widely but it is most advantageous to use about 1-5 percent by weight mlculated as sodium hypochlorite based on the weight of surfactant.

The permanganate bleaching step is preferably done at about room temperature, for example, at about 15- 30 C., although slight heating, say to about 50 C., may be used. The preferred concentration of permanganate, calculated as the potassium salt, is about 0.1-2.5 percent based on the weight of surfactant. With both hypohalite and permanganate, use of excessive bleaching agent provides no advantage and may result in some loss of bleaching efficiency. Since bleaching with permanganate involves corresponding reduction of the permanganate to precipitate manganese dioxide, it is necessary to remove the precipitated black oxide from the bleached surfactant solution. Any conventional means such as decantation or centrifuging can be used but ordinarily a. simple filtration is adequate.

The bleaching process is carried out in aqueous solu tion and for practical reasons, a relatively concentrated solution is preferred. Surfactant solutions of 20-50 percent concentration are illustrative. Similarly, the bleaching agents are best employed as dry solids or in relatively concentrated solution depending upon the particular compound involved.

EXAMPLES In the following examples, gram samples of 45% aqueous alkylated and sulfonated diphenyl ether were treated with aqueous sodium hypochloride, with potassium permanganate, and with combinations of the two sequentially or essentially simultaneously, each in various proportions as shown. Potassium permanganate was added as the powdered solid at about room temperature and the treated solution was filtered with a filter aid, usually diatomaceous earth, to remove precipitated manganese oxide. Sodium hypochlorite was added as a 15% aqueous solution and the mixture was then heated on a steam bath for about one hour. Color of the treated solutions was determined by comparison with a standard Gardner varnish color scale numbered with increasing color to a maximum value of 18.

The alkylated diphenyl ether sulfonates had been prepared according to known methods by alkylating diphenyl ether in the presence of a Friedel-Crafts catalyst such as AlCl with a suitable olefin, tetrapropylene and l-decene being those actually used, in proportions such that the diphenyl ether nucleus contained an average of 1-1.3 alkyl groups, and then sulfonating the product with 80;, to contain an average of 1.6-2 sulfonate groups per molecule.

EXAMPLES 1-2 Gardner color After After Sample Initial NaOCl KMn04 EXAMPLE 3 Samples of 45% aqueous disodium dodecyldiphenyl ether disulfonate (from tetrapropylene alkylate) were treated with different amounts of 15% aqueous NaOCl as described above and the treated solutions were then treated further with KMnO, as indicated. The untreated disulfonate solution was dark in color, having a Gardner color of 12. Quantities of NaOCl and KMnO, are calculated in weight percent of the compounds based on the dry weight of disulfonate in this and in Examples 4 and 5.-

N a 01 KMnOr Percent Color Percent Color EXAMPLE 4 The procedure of Example 3 was repeated in reverse, that is, the disulfonate solution was first treated with KMnO then with 15% aqueous NaOCl solution.

KMnO4 NaOCl Percent Color Percent Color 4 Evidently, differences in the quantity of KMnO, used initially had no significant effect on the final result. Use of more than 5% of NaOCl appeared to be somewhat harmful.

EXAMPLE 5 To a sample of 45% aqueous disodium dodecyldiphenyl ether disulfonate (from tetrapropylene alkylate) having Gardner color 12 there was added simultaneously 0.44% by weight of KMnO, (solid) and 3.33% of NaOCl (as a 15% aqueous solution). The mixture was heated on a steam bath for an hour, then it was cooled and filtered. The filtrate had a color of 4.5 on the Gardner scale.

-In contrast to the results presented above, another sample of the same disulfonate solution used in Example 5 was treated with 3.33% of NaOCl as above and 0.2% of hydrogen peroxide (30% aq.) (equivalent to 0.9% KMnO was added to the cooled solution. The bleached solution had a Gardner color of 6.5.

Using the procedure described in any of the above examples, other crude or undesirably colored alkylaryl sulfonates as previously defined are effectively bleached to obtain light colored products. In this way, sodium dodecylbenzenesulfonate, potassium nonylnaphthalenesulfonate, hexadecyltoluenesulfonic acid, and similar sulfonates are obtained as desirable white or off-white materials after bleaching with hypohalite and permanganate as shown.

I claim:

1. A process for bleaching an aqueous solution of an alkyl aryl sulfonate surfactant which comprises any combination of the steps:

(1) reacting by contacting an inorganic hypohalite with said solution, and

(2) reacting by contacting an inorganic permanganate with said solution and separating the resultant precipitated manganese oxide therefrom.

2. The process of claim 1 wherein the surfactant is an alkyldiphenyl ether sulfonate having an average of about 1-1.3 alkyl groups of 8-18 carbon atoms and an average of about 1.6-2 sulfonate groups per diphenyl ether nucleus.

3. The process of claim 2 wherein the surfactant is essentially n-decyldiphenyl ether disulfonate.

4. The process of claim 2 wherein the surfactant is essentially dodecyldiphenyl ether disulfonate.

5. The process of claim 2 wherein step (1) comprises contacting about 1-5% of sodium hypochlorite based on the weight of surfactant with the surfactant solution at about 40-100" C. and wherein step (2) comprises contacting about 0.1-2.5% of potassium permanganate based on the weight of surfactant with the surfactant solution at about l5-50 C. and separating the resultant precipitated manganese oxide therefrom.

6. The bleached surfactant product of the process of claim 1.

7. The bleached surfactant product of the process of claim 5.

References Cited UNITED STATES PATENTS 2,738,365 3/ 1956 Sylvester 252-99 XR 2,804,466 8/ 1957 Schurman 260-505 P XR 2,827,484 3/1958 Carlson et a1. 252-94 XR 3,142,691 7/1964 Wulfi et a1. 260-513 R MAYER WEINBLATI, Primary Examiner US. Cl. X.R. 

